The present invention relates to devices for dispensing, delivering, injecting, infusing or administering substances, and to methods of making and using such devices. More particularly, it relates to a device for administering a fluid product in doses. The device may be an injection apparatus, e.g., an injection pen.
Injection apparatus are known for example from diabetes therapy, administering growth hormones or osteoporosis preparations. Such apparatus should guarantee that the correct dosage is administered, yet should be simple and convenient to operate, two requirements which are particularly important when the user administers the relevant product him/herself.
An injection apparatus known from WO 01/10484 comprises a conveying and dosing means comprising a piston rod, a drive member and a two-member coupler consisting of a coupler input member and a coupler output member. The drive member is in threaded engagement with a casing of the injection apparatus and is coupled to the coupler output member via the coupler input member. The coupler output member is in another threaded engagement with the piston rod. The piston rod is guided axially and linearly by the casing, such that it is secured against rotating. For setting a dosage, the user rotates the drive member which, due to its threaded engagement with the casing, 30 then extends in the proximal direction, out of the casing. During this combined translational and rotational movement, the drive member slaves the coupler input member. The coupler input member is linearly guided on the coupler output member, such that it is secured against rotating, and together with the drive member forms a ratchet which allows the drive member to rotate relative to the coupler input member in one direction only. Once the desired dosage has been set, the user delivers it by pressing the drive member in the distal direction, into the casing. Due to the threaded engagement with the casing, the translational movement of the drive member is superimposed with a rotational movement which is transferred onto the coupler output member via the coupler input member. The rotational movement of the coupler output member advances the piston rod and therefore delivers the product. However, correcting a dosage which has been set too high proves awkward, for if the desired dosage has been exceeded while setting, the drive member has to be rotated up to a position corresponding to the maximum dosage. The coupler input member which is slaved during the combined translational and rotational movement of the drive member pushes against a translational stopper of the coupler output member when the drive member is in its maximum dosage position. Pulling further on the drive member releases the ratchet, and the arrangement consisting of the drive member and the coupler input member can be moved back in order to set the correct dosage. For correcting, the drive member has to be moved back into its ratchet engagement with the coupler input member.
While the drive force to be introduced into the conveying and dosing means for delivering still has to be manually applied in the injection apparatus of WO 01/10484, a conveying and dosing means follows from WO 02/053214 A1 which uses a drive spring for generating the drive force, wherein said drive spring is tensed by the setting the dosage and releases its stored energy during delivery. A spring which is wound around an axis in a spiral serves as the drive spring, the windings of which lie adjacently along the axis. Due to the coupling between the drive spring and the piston rod, only a fixedly predetermined dosage can be set.